According to a recent publication (Zebra Mussels: a 1992 Great Lakes Overview, the Great Lakes Sea Grant Network, 1992):
zebra mussels were discovered in the Great Lakes in 1988; PA1 since their discovery, they have been sighted in all of the great lakes and in the Hudson, Susquehanna, Ohio, Illinois, Tennessee and Mississippi river systems; PA1 scraping, once or twice a month, is the recommended method for removal from docks and piers, where a large buildup should be avoided because their waste products can cause damage; PA1 mussels can attach to outdrives of boats that remain in infested water, covering or entering water intakes, clogging cooling systems and damaging cooling system parts, and causing excessive drivetrain wear by attaching to props and shafts; PA1 mussels can attach to private and municipal water intakes, can even invade water systems and, in extreme cases, can completely clog household plumbing systems; and PA1 chlorination, at the point of raw water intake, has proved to be effective in controlling zebra mussels.
Zebra mussel infestation of water supply systems poses problems not only in terms of blockage of intake pipes but, more significantly, blockage of piping within the water system requiring, eventually, the replacement of all of the affected plumbing.